1. Field of the Invention
The present invention relates to noise filters equipped with two capacitors.
2. Description of the Related Art
A conventional technique, for example, Japanese patent laid open publication No. 2012-135175 has disclosed an electric power conversion device for boosting, i.e. increasing a direct current (DC) voltage, and/or decreasing a DC voltage, which is equipped with one or more noise filters. The noise filters decreases and removes a noise current. The noise filter is electrically connected to an input terminal and/or an output terminal of the electric power conversion device. The noise filter removes a noise current which would otherwise be transmitted from an external device into the inside of the electric power conversion device through the input terminal. A noise current generated in the electric power conversion device is also transmitted to the outside device through the output terminal. For example, the noise filter is generally comprised of a capacitor, a coil, and conducting wires connected to the electric components in the electric power conversion device.
However, there is a possibility that the noise filter composed of the capacitor and/or the conducting wires generates a noise current. That is, an electric power conversion circuit in the electric power conversion device has one or more electric components in which an alternating current (AC) flows. The flow of an AC current generates an AC magnetic field. Further, interaction between the generated AC magnetic field with the capacitor and the conducting wires generates a noise current (i.e. an induced noise current). The induced noise current is transmitted to the external device through the output terminal of the electric power conversion circuit. So, there is a strong demand to provide a noise filter having a function capable of preventing a large induced noise current from mixing with an output current of the electric power conversion device and being transmitted to the external device through the external terminal of the electric power conversion device even if an AC magnetic field is generated in the electric power conversion circuit.